1. Field of the Invention
The present invention relates to goniometers for measuring angles between body members and, more particularly, to a dual line protractor to measure the angle between two body members at a joint between the members at any desired orientation between the members.
2. Technical Background
The range of motion of a body joint is commonly measured to determine the presence and extent of joint abnormalities or the degree of healing and recovery from joint injuries. After a joint related injury a patient is often directed to limit the range of motion of a joint. Success of physical therapy and recovery is typically evaluated by improved ranges of motion of the injured joint. Goniometers are known which are adapted for measuring the range of motion of flexing joints such as knees, ankles, wrists, shoulders, hips, fingers, and the like. Early goniometers consisted of protractors with one fixed arm and one moveable arm. These devices were cumbersome, unreliable, and difficult to mount. They could interfere with the motion of the limb they were intended to measure and were not particularly useful. More recent devices using electronic means of measuring angular relationships suffer from similar problems. Some devices use a beam of energy, such as infrared light from a light emitting diode, reflectors, and detectors such as transistors. These electronic devices are complex, expensive, and can suffer from lack of accuracy and precision due to variations in the direction of the energy beam or consistent detection of an energy beam.
Protractors with chalk lines are known to mark lines at a given angle. These devices are accurate and precise over relatively long distances. They are easy to use, simple in construction, and inexpensive. Another advantage of these devices is that they use string lines which conform to irregularities of a surface without affecting precision or accuracy in setting an angle. However, they have not been adaptable as goniometers to measure angles of body members. What is needed is a line protractor that will measure body limb or member angles with the same ease and accuracy as obtained with protractor chalk lines that set angles.